1 /* Common capabilities, needed by capability.o. 2 * 3 * This program is free software; you can redistribute it and/or modify 4 * it under the terms of the GNU General Public License as published by 5 * the Free Software Foundation; either version 2 of the License, or 6 * (at your option) any later version. 7 * 8 */ 9 10 #include <linux/capability.h> 11 #include <linux/audit.h> 12 #include <linux/module.h> 13 #include <linux/init.h> 14 #include <linux/kernel.h> 15 #include <linux/lsm_hooks.h> 16 #include <linux/file.h> 17 #include <linux/mm.h> 18 #include <linux/mman.h> 19 #include <linux/pagemap.h> 20 #include <linux/swap.h> 21 #include <linux/skbuff.h> 22 #include <linux/netlink.h> 23 #include <linux/ptrace.h> 24 #include <linux/xattr.h> 25 #include <linux/hugetlb.h> 26 #include <linux/mount.h> 27 #include <linux/sched.h> 28 #include <linux/prctl.h> 29 #include <linux/securebits.h> 30 #include <linux/user_namespace.h> 31 #include <linux/binfmts.h> 32 #include <linux/personality.h> 33 34 /* 35 * If a non-root user executes a setuid-root binary in 36 * !secure(SECURE_NOROOT) mode, then we raise capabilities. 37 * However if fE is also set, then the intent is for only 38 * the file capabilities to be applied, and the setuid-root 39 * bit is left on either to change the uid (plausible) or 40 * to get full privilege on a kernel without file capabilities 41 * support. So in that case we do not raise capabilities. 42 * 43 * Warn if that happens, once per boot. 44 */ 45 static void warn_setuid_and_fcaps_mixed(const char *fname) 46 { 47 static int warned; 48 if (!warned) { 49 printk(KERN_INFO "warning: `%s' has both setuid-root and" 50 " effective capabilities. Therefore not raising all" 51 " capabilities.\n", fname); 52 warned = 1; 53 } 54 } 55 56 /** 57 * cap_capable - Determine whether a task has a particular effective capability 58 * @cred: The credentials to use 59 * @ns: The user namespace in which we need the capability 60 * @cap: The capability to check for 61 * @audit: Whether to write an audit message or not 62 * 63 * Determine whether the nominated task has the specified capability amongst 64 * its effective set, returning 0 if it does, -ve if it does not. 65 * 66 * NOTE WELL: cap_has_capability() cannot be used like the kernel's capable() 67 * and has_capability() functions. That is, it has the reverse semantics: 68 * cap_has_capability() returns 0 when a task has a capability, but the 69 * kernel's capable() and has_capability() returns 1 for this case. 70 */ 71 int cap_capable(const struct cred *cred, struct user_namespace *targ_ns, 72 int cap, int audit) 73 { 74 struct user_namespace *ns = targ_ns; 75 76 /* See if cred has the capability in the target user namespace 77 * by examining the target user namespace and all of the target 78 * user namespace's parents. 79 */ 80 for (;;) { 81 /* Do we have the necessary capabilities? */ 82 if (ns == cred->user_ns) 83 return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM; 84 85 /* Have we tried all of the parent namespaces? */ 86 if (ns == &init_user_ns) 87 return -EPERM; 88 89 /* 90 * The owner of the user namespace in the parent of the 91 * user namespace has all caps. 92 */ 93 if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid)) 94 return 0; 95 96 /* 97 * If you have a capability in a parent user ns, then you have 98 * it over all children user namespaces as well. 99 */ 100 ns = ns->parent; 101 } 102 103 /* We never get here */ 104 } 105 106 /** 107 * cap_settime - Determine whether the current process may set the system clock 108 * @ts: The time to set 109 * @tz: The timezone to set 110 * 111 * Determine whether the current process may set the system clock and timezone 112 * information, returning 0 if permission granted, -ve if denied. 113 */ 114 int cap_settime(const struct timespec *ts, const struct timezone *tz) 115 { 116 if (!capable(CAP_SYS_TIME)) 117 return -EPERM; 118 return 0; 119 } 120 121 /** 122 * cap_ptrace_access_check - Determine whether the current process may access 123 * another 124 * @child: The process to be accessed 125 * @mode: The mode of attachment. 126 * 127 * If we are in the same or an ancestor user_ns and have all the target 128 * task's capabilities, then ptrace access is allowed. 129 * If we have the ptrace capability to the target user_ns, then ptrace 130 * access is allowed. 131 * Else denied. 132 * 133 * Determine whether a process may access another, returning 0 if permission 134 * granted, -ve if denied. 135 */ 136 int cap_ptrace_access_check(struct task_struct *child, unsigned int mode) 137 { 138 int ret = 0; 139 const struct cred *cred, *child_cred; 140 141 rcu_read_lock(); 142 cred = current_cred(); 143 child_cred = __task_cred(child); 144 if (cred->user_ns == child_cred->user_ns && 145 cap_issubset(child_cred->cap_permitted, cred->cap_permitted)) 146 goto out; 147 if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE)) 148 goto out; 149 ret = -EPERM; 150 out: 151 rcu_read_unlock(); 152 return ret; 153 } 154 155 /** 156 * cap_ptrace_traceme - Determine whether another process may trace the current 157 * @parent: The task proposed to be the tracer 158 * 159 * If parent is in the same or an ancestor user_ns and has all current's 160 * capabilities, then ptrace access is allowed. 161 * If parent has the ptrace capability to current's user_ns, then ptrace 162 * access is allowed. 163 * Else denied. 164 * 165 * Determine whether the nominated task is permitted to trace the current 166 * process, returning 0 if permission is granted, -ve if denied. 167 */ 168 int cap_ptrace_traceme(struct task_struct *parent) 169 { 170 int ret = 0; 171 const struct cred *cred, *child_cred; 172 173 rcu_read_lock(); 174 cred = __task_cred(parent); 175 child_cred = current_cred(); 176 if (cred->user_ns == child_cred->user_ns && 177 cap_issubset(child_cred->cap_permitted, cred->cap_permitted)) 178 goto out; 179 if (has_ns_capability(parent, child_cred->user_ns, CAP_SYS_PTRACE)) 180 goto out; 181 ret = -EPERM; 182 out: 183 rcu_read_unlock(); 184 return ret; 185 } 186 187 /** 188 * cap_capget - Retrieve a task's capability sets 189 * @target: The task from which to retrieve the capability sets 190 * @effective: The place to record the effective set 191 * @inheritable: The place to record the inheritable set 192 * @permitted: The place to record the permitted set 193 * 194 * This function retrieves the capabilities of the nominated task and returns 195 * them to the caller. 196 */ 197 int cap_capget(struct task_struct *target, kernel_cap_t *effective, 198 kernel_cap_t *inheritable, kernel_cap_t *permitted) 199 { 200 const struct cred *cred; 201 202 /* Derived from kernel/capability.c:sys_capget. */ 203 rcu_read_lock(); 204 cred = __task_cred(target); 205 *effective = cred->cap_effective; 206 *inheritable = cred->cap_inheritable; 207 *permitted = cred->cap_permitted; 208 rcu_read_unlock(); 209 return 0; 210 } 211 212 /* 213 * Determine whether the inheritable capabilities are limited to the old 214 * permitted set. Returns 1 if they are limited, 0 if they are not. 215 */ 216 static inline int cap_inh_is_capped(void) 217 { 218 219 /* they are so limited unless the current task has the CAP_SETPCAP 220 * capability 221 */ 222 if (cap_capable(current_cred(), current_cred()->user_ns, 223 CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0) 224 return 0; 225 return 1; 226 } 227 228 /** 229 * cap_capset - Validate and apply proposed changes to current's capabilities 230 * @new: The proposed new credentials; alterations should be made here 231 * @old: The current task's current credentials 232 * @effective: A pointer to the proposed new effective capabilities set 233 * @inheritable: A pointer to the proposed new inheritable capabilities set 234 * @permitted: A pointer to the proposed new permitted capabilities set 235 * 236 * This function validates and applies a proposed mass change to the current 237 * process's capability sets. The changes are made to the proposed new 238 * credentials, and assuming no error, will be committed by the caller of LSM. 239 */ 240 int cap_capset(struct cred *new, 241 const struct cred *old, 242 const kernel_cap_t *effective, 243 const kernel_cap_t *inheritable, 244 const kernel_cap_t *permitted) 245 { 246 if (cap_inh_is_capped() && 247 !cap_issubset(*inheritable, 248 cap_combine(old->cap_inheritable, 249 old->cap_permitted))) 250 /* incapable of using this inheritable set */ 251 return -EPERM; 252 253 if (!cap_issubset(*inheritable, 254 cap_combine(old->cap_inheritable, 255 old->cap_bset))) 256 /* no new pI capabilities outside bounding set */ 257 return -EPERM; 258 259 /* verify restrictions on target's new Permitted set */ 260 if (!cap_issubset(*permitted, old->cap_permitted)) 261 return -EPERM; 262 263 /* verify the _new_Effective_ is a subset of the _new_Permitted_ */ 264 if (!cap_issubset(*effective, *permitted)) 265 return -EPERM; 266 267 new->cap_effective = *effective; 268 new->cap_inheritable = *inheritable; 269 new->cap_permitted = *permitted; 270 271 /* 272 * Mask off ambient bits that are no longer both permitted and 273 * inheritable. 274 */ 275 new->cap_ambient = cap_intersect(new->cap_ambient, 276 cap_intersect(*permitted, 277 *inheritable)); 278 if (WARN_ON(!cap_ambient_invariant_ok(new))) 279 return -EINVAL; 280 return 0; 281 } 282 283 /* 284 * Clear proposed capability sets for execve(). 285 */ 286 static inline void bprm_clear_caps(struct linux_binprm *bprm) 287 { 288 cap_clear(bprm->cred->cap_permitted); 289 bprm->cap_effective = false; 290 } 291 292 /** 293 * cap_inode_need_killpriv - Determine if inode change affects privileges 294 * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV 295 * 296 * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV 297 * affects the security markings on that inode, and if it is, should 298 * inode_killpriv() be invoked or the change rejected? 299 * 300 * Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and 301 * -ve to deny the change. 302 */ 303 int cap_inode_need_killpriv(struct dentry *dentry) 304 { 305 struct inode *inode = d_backing_inode(dentry); 306 int error; 307 308 if (!inode->i_op->getxattr) 309 return 0; 310 311 error = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, NULL, 0); 312 if (error <= 0) 313 return 0; 314 return 1; 315 } 316 317 /** 318 * cap_inode_killpriv - Erase the security markings on an inode 319 * @dentry: The inode/dentry to alter 320 * 321 * Erase the privilege-enhancing security markings on an inode. 322 * 323 * Returns 0 if successful, -ve on error. 324 */ 325 int cap_inode_killpriv(struct dentry *dentry) 326 { 327 struct inode *inode = d_backing_inode(dentry); 328 329 if (!inode->i_op->removexattr) 330 return 0; 331 332 return inode->i_op->removexattr(dentry, XATTR_NAME_CAPS); 333 } 334 335 /* 336 * Calculate the new process capability sets from the capability sets attached 337 * to a file. 338 */ 339 static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps, 340 struct linux_binprm *bprm, 341 bool *effective, 342 bool *has_cap) 343 { 344 struct cred *new = bprm->cred; 345 unsigned i; 346 int ret = 0; 347 348 if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE) 349 *effective = true; 350 351 if (caps->magic_etc & VFS_CAP_REVISION_MASK) 352 *has_cap = true; 353 354 CAP_FOR_EACH_U32(i) { 355 __u32 permitted = caps->permitted.cap[i]; 356 __u32 inheritable = caps->inheritable.cap[i]; 357 358 /* 359 * pP' = (X & fP) | (pI & fI) 360 * The addition of pA' is handled later. 361 */ 362 new->cap_permitted.cap[i] = 363 (new->cap_bset.cap[i] & permitted) | 364 (new->cap_inheritable.cap[i] & inheritable); 365 366 if (permitted & ~new->cap_permitted.cap[i]) 367 /* insufficient to execute correctly */ 368 ret = -EPERM; 369 } 370 371 /* 372 * For legacy apps, with no internal support for recognizing they 373 * do not have enough capabilities, we return an error if they are 374 * missing some "forced" (aka file-permitted) capabilities. 375 */ 376 return *effective ? ret : 0; 377 } 378 379 /* 380 * Extract the on-exec-apply capability sets for an executable file. 381 */ 382 int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps) 383 { 384 struct inode *inode = d_backing_inode(dentry); 385 __u32 magic_etc; 386 unsigned tocopy, i; 387 int size; 388 struct vfs_cap_data caps; 389 390 memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data)); 391 392 if (!inode || !inode->i_op->getxattr) 393 return -ENODATA; 394 395 size = inode->i_op->getxattr((struct dentry *)dentry, XATTR_NAME_CAPS, &caps, 396 XATTR_CAPS_SZ); 397 if (size == -ENODATA || size == -EOPNOTSUPP) 398 /* no data, that's ok */ 399 return -ENODATA; 400 if (size < 0) 401 return size; 402 403 if (size < sizeof(magic_etc)) 404 return -EINVAL; 405 406 cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc); 407 408 switch (magic_etc & VFS_CAP_REVISION_MASK) { 409 case VFS_CAP_REVISION_1: 410 if (size != XATTR_CAPS_SZ_1) 411 return -EINVAL; 412 tocopy = VFS_CAP_U32_1; 413 break; 414 case VFS_CAP_REVISION_2: 415 if (size != XATTR_CAPS_SZ_2) 416 return -EINVAL; 417 tocopy = VFS_CAP_U32_2; 418 break; 419 default: 420 return -EINVAL; 421 } 422 423 CAP_FOR_EACH_U32(i) { 424 if (i >= tocopy) 425 break; 426 cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted); 427 cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable); 428 } 429 430 cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK; 431 cpu_caps->inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK; 432 433 return 0; 434 } 435 436 /* 437 * Attempt to get the on-exec apply capability sets for an executable file from 438 * its xattrs and, if present, apply them to the proposed credentials being 439 * constructed by execve(). 440 */ 441 static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_cap) 442 { 443 int rc = 0; 444 struct cpu_vfs_cap_data vcaps; 445 446 bprm_clear_caps(bprm); 447 448 if (!file_caps_enabled) 449 return 0; 450 451 if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) 452 return 0; 453 454 rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps); 455 if (rc < 0) { 456 if (rc == -EINVAL) 457 printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n", 458 __func__, rc, bprm->filename); 459 else if (rc == -ENODATA) 460 rc = 0; 461 goto out; 462 } 463 464 rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_cap); 465 if (rc == -EINVAL) 466 printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n", 467 __func__, rc, bprm->filename); 468 469 out: 470 if (rc) 471 bprm_clear_caps(bprm); 472 473 return rc; 474 } 475 476 /** 477 * cap_bprm_set_creds - Set up the proposed credentials for execve(). 478 * @bprm: The execution parameters, including the proposed creds 479 * 480 * Set up the proposed credentials for a new execution context being 481 * constructed by execve(). The proposed creds in @bprm->cred is altered, 482 * which won't take effect immediately. Returns 0 if successful, -ve on error. 483 */ 484 int cap_bprm_set_creds(struct linux_binprm *bprm) 485 { 486 const struct cred *old = current_cred(); 487 struct cred *new = bprm->cred; 488 bool effective, has_cap = false, is_setid; 489 int ret; 490 kuid_t root_uid; 491 492 if (WARN_ON(!cap_ambient_invariant_ok(old))) 493 return -EPERM; 494 495 effective = false; 496 ret = get_file_caps(bprm, &effective, &has_cap); 497 if (ret < 0) 498 return ret; 499 500 root_uid = make_kuid(new->user_ns, 0); 501 502 if (!issecure(SECURE_NOROOT)) { 503 /* 504 * If the legacy file capability is set, then don't set privs 505 * for a setuid root binary run by a non-root user. Do set it 506 * for a root user just to cause least surprise to an admin. 507 */ 508 if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) { 509 warn_setuid_and_fcaps_mixed(bprm->filename); 510 goto skip; 511 } 512 /* 513 * To support inheritance of root-permissions and suid-root 514 * executables under compatibility mode, we override the 515 * capability sets for the file. 516 * 517 * If only the real uid is 0, we do not set the effective bit. 518 */ 519 if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) { 520 /* pP' = (cap_bset & ~0) | (pI & ~0) */ 521 new->cap_permitted = cap_combine(old->cap_bset, 522 old->cap_inheritable); 523 } 524 if (uid_eq(new->euid, root_uid)) 525 effective = true; 526 } 527 skip: 528 529 /* if we have fs caps, clear dangerous personality flags */ 530 if (!cap_issubset(new->cap_permitted, old->cap_permitted)) 531 bprm->per_clear |= PER_CLEAR_ON_SETID; 532 533 534 /* Don't let someone trace a set[ug]id/setpcap binary with the revised 535 * credentials unless they have the appropriate permit. 536 * 537 * In addition, if NO_NEW_PRIVS, then ensure we get no new privs. 538 */ 539 is_setid = !uid_eq(new->euid, old->uid) || !gid_eq(new->egid, old->gid); 540 541 if ((is_setid || 542 !cap_issubset(new->cap_permitted, old->cap_permitted)) && 543 bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) { 544 /* downgrade; they get no more than they had, and maybe less */ 545 if (!capable(CAP_SETUID) || 546 (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) { 547 new->euid = new->uid; 548 new->egid = new->gid; 549 } 550 new->cap_permitted = cap_intersect(new->cap_permitted, 551 old->cap_permitted); 552 } 553 554 new->suid = new->fsuid = new->euid; 555 new->sgid = new->fsgid = new->egid; 556 557 /* File caps or setid cancels ambient. */ 558 if (has_cap || is_setid) 559 cap_clear(new->cap_ambient); 560 561 /* 562 * Now that we've computed pA', update pP' to give: 563 * pP' = (X & fP) | (pI & fI) | pA' 564 */ 565 new->cap_permitted = cap_combine(new->cap_permitted, new->cap_ambient); 566 567 /* 568 * Set pE' = (fE ? pP' : pA'). Because pA' is zero if fE is set, 569 * this is the same as pE' = (fE ? pP' : 0) | pA'. 570 */ 571 if (effective) 572 new->cap_effective = new->cap_permitted; 573 else 574 new->cap_effective = new->cap_ambient; 575 576 if (WARN_ON(!cap_ambient_invariant_ok(new))) 577 return -EPERM; 578 579 bprm->cap_effective = effective; 580 581 /* 582 * Audit candidate if current->cap_effective is set 583 * 584 * We do not bother to audit if 3 things are true: 585 * 1) cap_effective has all caps 586 * 2) we are root 587 * 3) root is supposed to have all caps (SECURE_NOROOT) 588 * Since this is just a normal root execing a process. 589 * 590 * Number 1 above might fail if you don't have a full bset, but I think 591 * that is interesting information to audit. 592 */ 593 if (!cap_issubset(new->cap_effective, new->cap_ambient)) { 594 if (!cap_issubset(CAP_FULL_SET, new->cap_effective) || 595 !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) || 596 issecure(SECURE_NOROOT)) { 597 ret = audit_log_bprm_fcaps(bprm, new, old); 598 if (ret < 0) 599 return ret; 600 } 601 } 602 603 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS); 604 605 if (WARN_ON(!cap_ambient_invariant_ok(new))) 606 return -EPERM; 607 608 return 0; 609 } 610 611 /** 612 * cap_bprm_secureexec - Determine whether a secure execution is required 613 * @bprm: The execution parameters 614 * 615 * Determine whether a secure execution is required, return 1 if it is, and 0 616 * if it is not. 617 * 618 * The credentials have been committed by this point, and so are no longer 619 * available through @bprm->cred. 620 */ 621 int cap_bprm_secureexec(struct linux_binprm *bprm) 622 { 623 const struct cred *cred = current_cred(); 624 kuid_t root_uid = make_kuid(cred->user_ns, 0); 625 626 if (!uid_eq(cred->uid, root_uid)) { 627 if (bprm->cap_effective) 628 return 1; 629 if (!cap_issubset(cred->cap_permitted, cred->cap_ambient)) 630 return 1; 631 } 632 633 return (!uid_eq(cred->euid, cred->uid) || 634 !gid_eq(cred->egid, cred->gid)); 635 } 636 637 /** 638 * cap_inode_setxattr - Determine whether an xattr may be altered 639 * @dentry: The inode/dentry being altered 640 * @name: The name of the xattr to be changed 641 * @value: The value that the xattr will be changed to 642 * @size: The size of value 643 * @flags: The replacement flag 644 * 645 * Determine whether an xattr may be altered or set on an inode, returning 0 if 646 * permission is granted, -ve if denied. 647 * 648 * This is used to make sure security xattrs don't get updated or set by those 649 * who aren't privileged to do so. 650 */ 651 int cap_inode_setxattr(struct dentry *dentry, const char *name, 652 const void *value, size_t size, int flags) 653 { 654 if (!strcmp(name, XATTR_NAME_CAPS)) { 655 if (!capable(CAP_SETFCAP)) 656 return -EPERM; 657 return 0; 658 } 659 660 if (!strncmp(name, XATTR_SECURITY_PREFIX, 661 sizeof(XATTR_SECURITY_PREFIX) - 1) && 662 !capable(CAP_SYS_ADMIN)) 663 return -EPERM; 664 return 0; 665 } 666 667 /** 668 * cap_inode_removexattr - Determine whether an xattr may be removed 669 * @dentry: The inode/dentry being altered 670 * @name: The name of the xattr to be changed 671 * 672 * Determine whether an xattr may be removed from an inode, returning 0 if 673 * permission is granted, -ve if denied. 674 * 675 * This is used to make sure security xattrs don't get removed by those who 676 * aren't privileged to remove them. 677 */ 678 int cap_inode_removexattr(struct dentry *dentry, const char *name) 679 { 680 if (!strcmp(name, XATTR_NAME_CAPS)) { 681 if (!capable(CAP_SETFCAP)) 682 return -EPERM; 683 return 0; 684 } 685 686 if (!strncmp(name, XATTR_SECURITY_PREFIX, 687 sizeof(XATTR_SECURITY_PREFIX) - 1) && 688 !capable(CAP_SYS_ADMIN)) 689 return -EPERM; 690 return 0; 691 } 692 693 /* 694 * cap_emulate_setxuid() fixes the effective / permitted capabilities of 695 * a process after a call to setuid, setreuid, or setresuid. 696 * 697 * 1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of 698 * {r,e,s}uid != 0, the permitted and effective capabilities are 699 * cleared. 700 * 701 * 2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective 702 * capabilities of the process are cleared. 703 * 704 * 3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective 705 * capabilities are set to the permitted capabilities. 706 * 707 * fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should 708 * never happen. 709 * 710 * -astor 711 * 712 * cevans - New behaviour, Oct '99 713 * A process may, via prctl(), elect to keep its capabilities when it 714 * calls setuid() and switches away from uid==0. Both permitted and 715 * effective sets will be retained. 716 * Without this change, it was impossible for a daemon to drop only some 717 * of its privilege. The call to setuid(!=0) would drop all privileges! 718 * Keeping uid 0 is not an option because uid 0 owns too many vital 719 * files.. 720 * Thanks to Olaf Kirch and Peter Benie for spotting this. 721 */ 722 static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old) 723 { 724 kuid_t root_uid = make_kuid(old->user_ns, 0); 725 726 if ((uid_eq(old->uid, root_uid) || 727 uid_eq(old->euid, root_uid) || 728 uid_eq(old->suid, root_uid)) && 729 (!uid_eq(new->uid, root_uid) && 730 !uid_eq(new->euid, root_uid) && 731 !uid_eq(new->suid, root_uid))) { 732 if (!issecure(SECURE_KEEP_CAPS)) { 733 cap_clear(new->cap_permitted); 734 cap_clear(new->cap_effective); 735 } 736 737 /* 738 * Pre-ambient programs expect setresuid to nonroot followed 739 * by exec to drop capabilities. We should make sure that 740 * this remains the case. 741 */ 742 cap_clear(new->cap_ambient); 743 } 744 if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid)) 745 cap_clear(new->cap_effective); 746 if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid)) 747 new->cap_effective = new->cap_permitted; 748 } 749 750 /** 751 * cap_task_fix_setuid - Fix up the results of setuid() call 752 * @new: The proposed credentials 753 * @old: The current task's current credentials 754 * @flags: Indications of what has changed 755 * 756 * Fix up the results of setuid() call before the credential changes are 757 * actually applied, returning 0 to grant the changes, -ve to deny them. 758 */ 759 int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags) 760 { 761 switch (flags) { 762 case LSM_SETID_RE: 763 case LSM_SETID_ID: 764 case LSM_SETID_RES: 765 /* juggle the capabilities to follow [RES]UID changes unless 766 * otherwise suppressed */ 767 if (!issecure(SECURE_NO_SETUID_FIXUP)) 768 cap_emulate_setxuid(new, old); 769 break; 770 771 case LSM_SETID_FS: 772 /* juggle the capabilties to follow FSUID changes, unless 773 * otherwise suppressed 774 * 775 * FIXME - is fsuser used for all CAP_FS_MASK capabilities? 776 * if not, we might be a bit too harsh here. 777 */ 778 if (!issecure(SECURE_NO_SETUID_FIXUP)) { 779 kuid_t root_uid = make_kuid(old->user_ns, 0); 780 if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid)) 781 new->cap_effective = 782 cap_drop_fs_set(new->cap_effective); 783 784 if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid)) 785 new->cap_effective = 786 cap_raise_fs_set(new->cap_effective, 787 new->cap_permitted); 788 } 789 break; 790 791 default: 792 return -EINVAL; 793 } 794 795 return 0; 796 } 797 798 /* 799 * Rationale: code calling task_setscheduler, task_setioprio, and 800 * task_setnice, assumes that 801 * . if capable(cap_sys_nice), then those actions should be allowed 802 * . if not capable(cap_sys_nice), but acting on your own processes, 803 * then those actions should be allowed 804 * This is insufficient now since you can call code without suid, but 805 * yet with increased caps. 806 * So we check for increased caps on the target process. 807 */ 808 static int cap_safe_nice(struct task_struct *p) 809 { 810 int is_subset, ret = 0; 811 812 rcu_read_lock(); 813 is_subset = cap_issubset(__task_cred(p)->cap_permitted, 814 current_cred()->cap_permitted); 815 if (!is_subset && !ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) 816 ret = -EPERM; 817 rcu_read_unlock(); 818 819 return ret; 820 } 821 822 /** 823 * cap_task_setscheduler - Detemine if scheduler policy change is permitted 824 * @p: The task to affect 825 * 826 * Detemine if the requested scheduler policy change is permitted for the 827 * specified task, returning 0 if permission is granted, -ve if denied. 828 */ 829 int cap_task_setscheduler(struct task_struct *p) 830 { 831 return cap_safe_nice(p); 832 } 833 834 /** 835 * cap_task_ioprio - Detemine if I/O priority change is permitted 836 * @p: The task to affect 837 * @ioprio: The I/O priority to set 838 * 839 * Detemine if the requested I/O priority change is permitted for the specified 840 * task, returning 0 if permission is granted, -ve if denied. 841 */ 842 int cap_task_setioprio(struct task_struct *p, int ioprio) 843 { 844 return cap_safe_nice(p); 845 } 846 847 /** 848 * cap_task_ioprio - Detemine if task priority change is permitted 849 * @p: The task to affect 850 * @nice: The nice value to set 851 * 852 * Detemine if the requested task priority change is permitted for the 853 * specified task, returning 0 if permission is granted, -ve if denied. 854 */ 855 int cap_task_setnice(struct task_struct *p, int nice) 856 { 857 return cap_safe_nice(p); 858 } 859 860 /* 861 * Implement PR_CAPBSET_DROP. Attempt to remove the specified capability from 862 * the current task's bounding set. Returns 0 on success, -ve on error. 863 */ 864 static int cap_prctl_drop(unsigned long cap) 865 { 866 struct cred *new; 867 868 if (!ns_capable(current_user_ns(), CAP_SETPCAP)) 869 return -EPERM; 870 if (!cap_valid(cap)) 871 return -EINVAL; 872 873 new = prepare_creds(); 874 if (!new) 875 return -ENOMEM; 876 cap_lower(new->cap_bset, cap); 877 return commit_creds(new); 878 } 879 880 /** 881 * cap_task_prctl - Implement process control functions for this security module 882 * @option: The process control function requested 883 * @arg2, @arg3, @arg4, @arg5: The argument data for this function 884 * 885 * Allow process control functions (sys_prctl()) to alter capabilities; may 886 * also deny access to other functions not otherwise implemented here. 887 * 888 * Returns 0 or +ve on success, -ENOSYS if this function is not implemented 889 * here, other -ve on error. If -ENOSYS is returned, sys_prctl() and other LSM 890 * modules will consider performing the function. 891 */ 892 int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3, 893 unsigned long arg4, unsigned long arg5) 894 { 895 const struct cred *old = current_cred(); 896 struct cred *new; 897 898 switch (option) { 899 case PR_CAPBSET_READ: 900 if (!cap_valid(arg2)) 901 return -EINVAL; 902 return !!cap_raised(old->cap_bset, arg2); 903 904 case PR_CAPBSET_DROP: 905 return cap_prctl_drop(arg2); 906 907 /* 908 * The next four prctl's remain to assist with transitioning a 909 * system from legacy UID=0 based privilege (when filesystem 910 * capabilities are not in use) to a system using filesystem 911 * capabilities only - as the POSIX.1e draft intended. 912 * 913 * Note: 914 * 915 * PR_SET_SECUREBITS = 916 * issecure_mask(SECURE_KEEP_CAPS_LOCKED) 917 * | issecure_mask(SECURE_NOROOT) 918 * | issecure_mask(SECURE_NOROOT_LOCKED) 919 * | issecure_mask(SECURE_NO_SETUID_FIXUP) 920 * | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED) 921 * 922 * will ensure that the current process and all of its 923 * children will be locked into a pure 924 * capability-based-privilege environment. 925 */ 926 case PR_SET_SECUREBITS: 927 if ((((old->securebits & SECURE_ALL_LOCKS) >> 1) 928 & (old->securebits ^ arg2)) /*[1]*/ 929 || ((old->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/ 930 || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/ 931 || (cap_capable(current_cred(), 932 current_cred()->user_ns, CAP_SETPCAP, 933 SECURITY_CAP_AUDIT) != 0) /*[4]*/ 934 /* 935 * [1] no changing of bits that are locked 936 * [2] no unlocking of locks 937 * [3] no setting of unsupported bits 938 * [4] doing anything requires privilege (go read about 939 * the "sendmail capabilities bug") 940 */ 941 ) 942 /* cannot change a locked bit */ 943 return -EPERM; 944 945 new = prepare_creds(); 946 if (!new) 947 return -ENOMEM; 948 new->securebits = arg2; 949 return commit_creds(new); 950 951 case PR_GET_SECUREBITS: 952 return old->securebits; 953 954 case PR_GET_KEEPCAPS: 955 return !!issecure(SECURE_KEEP_CAPS); 956 957 case PR_SET_KEEPCAPS: 958 if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */ 959 return -EINVAL; 960 if (issecure(SECURE_KEEP_CAPS_LOCKED)) 961 return -EPERM; 962 963 new = prepare_creds(); 964 if (!new) 965 return -ENOMEM; 966 if (arg2) 967 new->securebits |= issecure_mask(SECURE_KEEP_CAPS); 968 else 969 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS); 970 return commit_creds(new); 971 972 case PR_CAP_AMBIENT: 973 if (arg2 == PR_CAP_AMBIENT_CLEAR_ALL) { 974 if (arg3 | arg4 | arg5) 975 return -EINVAL; 976 977 new = prepare_creds(); 978 if (!new) 979 return -ENOMEM; 980 cap_clear(new->cap_ambient); 981 return commit_creds(new); 982 } 983 984 if (((!cap_valid(arg3)) | arg4 | arg5)) 985 return -EINVAL; 986 987 if (arg2 == PR_CAP_AMBIENT_IS_SET) { 988 return !!cap_raised(current_cred()->cap_ambient, arg3); 989 } else if (arg2 != PR_CAP_AMBIENT_RAISE && 990 arg2 != PR_CAP_AMBIENT_LOWER) { 991 return -EINVAL; 992 } else { 993 if (arg2 == PR_CAP_AMBIENT_RAISE && 994 (!cap_raised(current_cred()->cap_permitted, arg3) || 995 !cap_raised(current_cred()->cap_inheritable, 996 arg3) || 997 issecure(SECURE_NO_CAP_AMBIENT_RAISE))) 998 return -EPERM; 999 1000 new = prepare_creds(); 1001 if (!new) 1002 return -ENOMEM; 1003 if (arg2 == PR_CAP_AMBIENT_RAISE) 1004 cap_raise(new->cap_ambient, arg3); 1005 else 1006 cap_lower(new->cap_ambient, arg3); 1007 return commit_creds(new); 1008 } 1009 1010 default: 1011 /* No functionality available - continue with default */ 1012 return -ENOSYS; 1013 } 1014 } 1015 1016 /** 1017 * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted 1018 * @mm: The VM space in which the new mapping is to be made 1019 * @pages: The size of the mapping 1020 * 1021 * Determine whether the allocation of a new virtual mapping by the current 1022 * task is permitted, returning 1 if permission is granted, 0 if not. 1023 */ 1024 int cap_vm_enough_memory(struct mm_struct *mm, long pages) 1025 { 1026 int cap_sys_admin = 0; 1027 1028 if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN, 1029 SECURITY_CAP_NOAUDIT) == 0) 1030 cap_sys_admin = 1; 1031 return cap_sys_admin; 1032 } 1033 1034 /* 1035 * cap_mmap_addr - check if able to map given addr 1036 * @addr: address attempting to be mapped 1037 * 1038 * If the process is attempting to map memory below dac_mmap_min_addr they need 1039 * CAP_SYS_RAWIO. The other parameters to this function are unused by the 1040 * capability security module. Returns 0 if this mapping should be allowed 1041 * -EPERM if not. 1042 */ 1043 int cap_mmap_addr(unsigned long addr) 1044 { 1045 int ret = 0; 1046 1047 if (addr < dac_mmap_min_addr) { 1048 ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO, 1049 SECURITY_CAP_AUDIT); 1050 /* set PF_SUPERPRIV if it turns out we allow the low mmap */ 1051 if (ret == 0) 1052 current->flags |= PF_SUPERPRIV; 1053 } 1054 return ret; 1055 } 1056 1057 int cap_mmap_file(struct file *file, unsigned long reqprot, 1058 unsigned long prot, unsigned long flags) 1059 { 1060 return 0; 1061 } 1062 1063 #ifdef CONFIG_SECURITY 1064 1065 struct security_hook_list capability_hooks[] = { 1066 LSM_HOOK_INIT(capable, cap_capable), 1067 LSM_HOOK_INIT(settime, cap_settime), 1068 LSM_HOOK_INIT(ptrace_access_check, cap_ptrace_access_check), 1069 LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme), 1070 LSM_HOOK_INIT(capget, cap_capget), 1071 LSM_HOOK_INIT(capset, cap_capset), 1072 LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds), 1073 LSM_HOOK_INIT(bprm_secureexec, cap_bprm_secureexec), 1074 LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv), 1075 LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv), 1076 LSM_HOOK_INIT(mmap_addr, cap_mmap_addr), 1077 LSM_HOOK_INIT(mmap_file, cap_mmap_file), 1078 LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid), 1079 LSM_HOOK_INIT(task_prctl, cap_task_prctl), 1080 LSM_HOOK_INIT(task_setscheduler, cap_task_setscheduler), 1081 LSM_HOOK_INIT(task_setioprio, cap_task_setioprio), 1082 LSM_HOOK_INIT(task_setnice, cap_task_setnice), 1083 LSM_HOOK_INIT(vm_enough_memory, cap_vm_enough_memory), 1084 }; 1085 1086 void __init capability_add_hooks(void) 1087 { 1088 security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks)); 1089 } 1090 1091 #endif /* CONFIG_SECURITY */ 1092